The term "shock absorber" is somewhat less than accurate. It is a spring which absorbs shock by distributing the force over a long time period and distance. The "Shock absorber's" principal function is to damp the suspension movement, both on upward bounce and resulting rebound. It does so by converting the kinetic energy of suspension movement to thermal energy; the heat so generated is dissipated to the atmosphere or the car's chassis. Shock absorber design is intimately connected to that of the suspension system in toto, tires, springs, chassis, and their linking components.
The passive shock absorber system which dissipates or damps the relative movement between the tire or unsprung mass and the chassis or sprung mass is a passive system which, to date, was adequate as a motor vehicle suspension component. Automobile manufacturers relied upon the great mass of present day automobiles to aid in the damping function of the passive suspension system. With the advent of the "energy crisis", the tendency is to drastically reduce the mass of future automobiles to a point where they will weigh less than half the weight of current day versions. Unless automobile suspension systems can be drastically redesigned and modified, the smooth riding characteristics traditionally associated with today's heavy automobiles could no longer be realized.
Design of a shock absorber must take into account the many variations of road surface, vehicle speed and vehicle load. One has only to follow an empty flatbed trailer to appreciate the contribution of these variables to axle hop and control. Since the shock absorber has no support function in the suspension, its design does not affect steady state conditions per se. Even here, though, the transients leading to these conditions--body roll, understeer and oversteer--can be affected by shock absorber specification.
The classical system employed in most automotive vehicles today is a passive system in which a spring and a shock absorber are arranged in parallel between the sprung and unsprung masses. At high frequencies of disturbance or at the arrival of a bump in the course of travel, the shock absorber acts as a stiff member. Hence, sudden acceleration of the unsprung mass or wheel hits the passenger compartment almost unmitigated. Theoretically, an improved system would consist of placing a shock absorber and spring in series for a high frequency disturbance would be absorbed by the spring independent of the stiffness of the shock absorber. However, a shock absorber cannot sustain any static load unless a second spring is placed in parallel with it to act as a lever.
Accordingly, it is an object of the present invention to provide an automobile suspension system which eliminates the disadvantages outlined above.
Another object of the present invention is to provide a vehicle suspension system wherein several springs and shock absorber members are configured to greatly improve the suspension qualities of the system.
Yet another object of the present invention is to provide a vehicle suspension system wherein a relatively low mass vehicle can be caused to exhibit a feel and ride comparable to a vehicle of much heavier mass.
Still another object of the present invention is to provide a vehicle suspension system which at least partially compensates for centrifugal force while the vehicle is cornering a horizontal corner and can be used to at least partially compensate for an incline as an aid in maintaining the vehicle in a horizontal plane.
A further object of the present invention is to provide a vehicle suspension system which acts to greatly reduce the characteristic motion of a vehicle when exposed to a sudden breaking action.
Quite generally, the suspension system of the present invention is used in an automobile or other type of vehicle having a frame, a wheel and movable support for said wheel. The suspension system is comprised of four basic elements:
1. A first shock absorbing member functionally connected to the wheel support having upper and lower fluid-containing chambers separated by a piston and possessing control means capable of connecting and partially disconnecting the fluid chambers.
2. A first spring means arranged in parallel with the first shock absorbing member and functionally connected to the wheel support.
3. A second shock absorbing member functionally connected to the vehicle frame and arranged in series with the first shock absorbing member and the first spring means.
4. A second spring means arranged in parallel with the second shock absorber member and in one embodiment in series with the first shock absorbing member and first spring means and in parallel with these elements in a second embodiment.
In order to provide for increased comfort, the first spring means is designed to have a greater spring stiffness than the second spring means; optimally, the second spring means should possess a spring stiffness of only approximately 20% of the spring stiffness of the first spring means.
Using various controls, which will be explained later, the suspension system is designed so that whenever the first shock absorbing member and first spring means are expanding the control means causes the fluid chambers within the first shock absorbing member to at least partially disconnect whenever the vehicle frame is vertically rising and to connect the various fluid chambers whenever the vehicle frame is vertically falling.
Conversely, the suspension system of the present invention is defined so that whenever the first shock absorbing member and first spring means are being compressed, the control means is caused to at least partially disconnect the fluid chambers from one another whenever the vehicle frame is vertically falling and to connect the fluid chambers whenever the vehicle frame is vertically rising.